1, solution: because the perimeter of the bottom is 12.56cm, so R=2cm, (I think your 12.26 is wrong! )

Cut into three small cylinders with the same size horizontally, and then increase the surface area by four round bottoms.

So the surface area increased by 4×(3. 14×2×2)=50.24cm.

2. The circumference of the bottom of cylindrical wood is 3 1.4cm, so R=5cm, so h= 10cm.

So, V=( 1/3)3. 14×5? × 10 =26 1.67cm？